A backward wave oscillator (BWO) is a tunable source of coherent radiation. In a conventional backward oscillator an electron gun sends a beam of electrons into a slow-wave structure. The output power of the electron beam is extracted near the electron gun. Because of their wide tuning range, the backward wave oscillators have been used in a variety of applications including as local oscillators in heterodyne receivers for the detection of sub mm radiation.
Nominally, the sub mm wave regime ranges from 300 to 3000 GHz where electromagnetic radiation has a wavelength between 1.0 and 0.1 mm. Above the sub mm band is the infrared region where wavelengths are typically reported in microns and the electromagnetic waves behave similar to light waves. Below the sub mm band is the mm wave band (ranging from 30 to 300 GHz) and the microwave band (ranging from 1 to 30 GHz). In the mm and microwave bands, the electromagnetic waves behave similar to the ordinary low frequency electric currents and voltages with the very important distinction that the circuit dimensions are comparable to a wavelength. In the sub mm band, electromagnetic radiation has the properties of both microwaves and light. Structures that are suitable for microwaves become unreasonably small for sub mm devices while standard optical configurations become far too large.
Added to the dimensional complexity are several physical constraints in the sub mm band imposed by significant atmospheric attenuation and by greatly increased electrical conduction losses. Atmospheric attenuation is greatly enhanced by the presence of vibrational and rotational resonances of naturally occurring molecular gasses, while the roughness of metal surfaces significantly increases conduction losses. Because many of the issues regarding size and losses become exceedingly important at frequencies well below 300 GHz, the sub mm regime is frequently extended to 100 GHz.
Conventionally, vacuum electron devices have dominated the microwave and mm wave regimes for applications where power and efficiency are important system parameters. However, within the sub mm regime, conventional microwave structures are usually not applicable. Solid state devices are used as low power signal sources in the microwave and low mm wave regimes, but are not applicable in the sub mm band. Gas lasers can be operated in the sub mm band, but they can only be tuned to discrete frequencies and they are generally very large devices. Presently, there is no commercially available electronically tunable signal source in the sub mm band.
Therefore, an object of the instant disclosure is to provide a BWO having an interdigital slow-wave circuit.
Another object is to provide a BWO comprising diamond.
Still another object of the disclosure is to provide a novel spatial relationship between the electron beam of a BWO and the slow-wave circuit.
Another object of the disclosure is to provide a BWO having an interaction impedance of greater than 1, preferably greater than 10 and most preferably greater than 100.
A further object of the disclosure is to provide a miniature BWO weighing less than 10 kg and preferably less than 1 kg.
A still further object of the disclosure is to provide an interdigital circuit for use in a BWO.
Still another object of the disclosure is to provide a BWO structure integrated with an electron source.
A further object of the disclosure is to provide a coupling interface between an electron source and the BWO.
Another object of the disclosure is to provide an integrated BWO having field emission cathode as an electron source.
A still further object of the disclosure is to provide a BWO having an electron beam positioned between a first plane and a second plane; each of the first and the second plane defining at least one of a focus electrode, a first anode, a second anode (or a slow-wave circuit) and one or more collector.
Another object of the disclosure is to provide an apparatus comprising an electron source directing an electron beam to a focus electrode, a first anode and a second anode, whereby the electrons are collected by one or more collectors.
Still another object is to disclose a method for fabricating a BWO having an interdigital circuit.
Still another object of the disclosures is to provide a BWO where the electron source and the interdigital circuit are fabricated of the same diamond.
In still another embodiment, the disclosure relates to an electron gun integrated with a slow-wave circuit.
A still further object of the disclosure is to provide a BWO requiring a substantially lower operation voltage as compared with the conventional BWO.
A further object of the disclosure is to provide a BWO having substantially higher interaction efficiency between the slow-wave guide and the electron beam.
These and other objects will be discussed in relation with the following drawings.